NXP Semiconductors K32 L2A Series, Reference Manual, Page: 1212 / 1379

INTERFACE
TRNG
SA-RNG
OSC
SA-RNG-WRAPPER
Figure 48-1. SA TRNG Block Diagram
48.1.2 TRNG Functional Description.
The TRNG consists of several functional sub-modules. Its overall functionality can be
easily described from the top level in terms of generating entropy for seed generation.
The functionality of each sub-module is briefly described in the following subsections.
TRNG is based on collecting bits from a random noise source. This random noise source
is a ring oscillator that is sensitive to random noise (temperature variations, voltage
variations, cross-talk and other random noise) within the device in which the TRNG is
used. This noise causes various small changes in the period of the oscillator. Therefore, if
the count of the ring oscillator clock cycles is sampled after a known period of time, this
count will vary each time the sample is taken. By using the variance in this count over a
large number of samples, random bits can be derived.
The TRNG comprises two entropy sources, each of which provides a single bit of output.
Concatenated together, these 2 output bits are expected to provide 1 bit of entropy every
100 clock cycles. In addition to generating entropy, the TRNG also performs several
statistical tests on its output.
Standalone True Random Number Generator (SA-TRNG).
K32 L2A Reference Manual, Rev. 2, 01/2020
1212 NXP Semiconductors